Without monitoring ambient noise levels, it's impossible to measure hearing thresholds accurately. Uncontrolled environmental noise can cause patients to misinterpret test stimuli, leading to false responses or invalid results.
However, by maintaining ambient noise within certain limits, it's possible to mitigate these interferences - which can be the difference between a pass or a referral for a patient.
Monitoring ambient noise is the simple process of measuring the level of background noise in the hearing test environment. This essentially leads to better diagnosis and treatment outcomes.
Why measure ambient noise
- To prevent interference with test tones - Background noise can interfere with test tones, leading to artificially elevated hearing thresholds. This can result in a healthcare professional underestimating a patient's hearing ability or misdiagnosing hearing loss.
- Compliance with standards - Organisations like ANSI (American National Standards Institute), ISO (International Organization for Standardization), and OSHA (Occupational Safety and Health Administration), set specific noise level requirements for audiometric testing environments. Measuring ambient noise ensures compliance with these standards.
- To ensure test validity and consistency - Variations in ambient noise can cause inconsistencies in test results. Monitoring noise levels helps maintain a controlled testing environment, improving the reliability of hearing assessments.
- To be able to adjust test setting conditions if needed - If ambient noise exceeds acceptable levels, adjustments can be made by using noise-reducing headphones, relocating the test, or rescheduling it for a quieter time.
- Mobile and occupational audiometry - In non-clinical settings like workplace screenings, noise levels can fluctuate because of machinery, conversations, or outdoor sounds. Continuous noise monitoring ensures test accuracy in these environments.
What to use for measuring ambient noise
Ambient noise can be measured with a sound level meter or sound room microphone. This measures the frequency content in octave or third-octave bands. It's important to remember that a certain degree of ‘measurement uncertainty’ exists from sources such as the environment (ambient noise and distractions), equipment, subject, method and tester.
What noise is permissible?
The British Society of Audiology recommends that “In general, the ambient noise should not exceed 35 dBA” (BSA, 2017). But maximum permissible ambient sound pressure levels should be (SPL) - BS EN ISO 8253-1.
| Test tone frequency range |
Earphone attenuation |
Lowest hearing threshold level to be measured |
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Noise with energy at low frequencies can mask test tones at higher frequencies. Often referred to as the ‘upward spread of masking’.
Low frequency test tones require a quieter test environment.
The 500 - 8000kHz test tone range used for surveillance audiometry permits more ambient noise.
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The maximum permissible ambient SPLs are based on an average earphone attenuation.
Supra-aural earphones give the least attenuation so require a quieter test environment.
Some listeners will receive less than average attenuation.
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0 dB HL is based on the median thresholds of otologically normal 18 – 25 year olds.
Half of those will have thresholds better than 0 dB HL.
Maximum permissible ambient SPLs must be reduced to measure their baseline.
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How to avoid exceeding SPLs
- Measure the levels in the test room under representative conditions
- Get the average sound reduction data for the earphones. If this data is not in BS EN ISO 8253-1, check the audiometer or earphone instruction manual
- Calculate the difference in attenuation** between the earphone and the typical current supra-aural earphone values in BS EN ISO 8253-1
- Add the difference values to the highest allowed ambient noise levels. These levels are for typical supra-aural earphones. Refer to BS EN ISO 8253-1 for more information
- Compare the result with the levels measured in the test room.
* Required for conformance with BS EN ISO 8253-1
** Interpolation may be required for octave band attenuation data
Ambient noise monitoring solutions
Adding a Sound Room Microphone (SRM) to your test process allows you to monitor the test environment, providing you with complete confidence in the quality of your audiometry results. At Amplivox we offer several solutions that include SRM technology:
The AnovaTM delivers unmatched accuracy with the option of an external SRM. The microphone is placed in the test environment, providing live feedback when noise exceeds the ‘ideal level’ for accurate measurements. Enabling you to achieve the best possible test conditions.
Our modelONE pc-based audiometer consists of noise-attenuating headphones with the inclusion of an in-built SRM.
For more information about which of our devices include ambient noise level monitoring, please contact our customer support team. You can contact us on +44 (0)1865 880 846 or by email.
Resources
Health and Safety Executive, Health Surveillance: https://www.hse.gov.uk/noise/healthsurveillance.htm
British Society of Audiology: https://www.thebsa.org.uk/
American National Standards Institute: https://www.ansi.org/
International Organization for Standardization: https://www.iso.org/home.html
Occupational Safety and Health Administration: https://www.osha.gov/